It is well known that artists who paint on canvas or the like do so in a great variety of colors and therefore employ brushes of various widths. They also are faced with having to switch their brushes many times as they progress with a painting. As a result at the end of a painting session they are faced with considerable clean up problems as they cannot leave their brushes in a wet state as the paint will harden and the brush will become useless.
Therefore, artists must laboriously go through the stages of cleaning their brushes by dipping and swirling them in small vessels of a solvent, then expressing the solvent laden brush and then as a final step to remove the last vestiges of solvent, strike the bristle portion of the brush against a hard surface thereby releasing droplets of solvent in a shower. The droplets so released will fall or fly in any uncontrolled direction and if in a free environment will mess up with droplets the first object in its path.